A terrible band that takes a synthesizer and 2 microphones and a computer and makes millions of dollars from poorly written lyrics and said tools. Their hit song, Party Rock Anthem, neither sounds like a party or rock, more like a rave or hemorrhaging piece of shit. Do not listen to them. Their only half-decent song is I Am Not a Whore, and that's like picking the cleanest dirty shirt in a shit-pile.

Jim: "Hey did you hear the new LMFAO song?"
Al: "No I have a taste in music and you sound like a 13 year old girl."

Abbreviated form of "Laughing my fucking arse (or ass or other) off" commonly used in online/networked gaming and in chat rooms, similar to, though more expressive and indicating greater laughment than lmao (laughing my arse (etc.) off).